Wireless location determination techniques can use base stations or devices emitting radio signals to a mobile terminal to determine its position. Signals can also be emitted from the mobile terminal (device) to the base station. To locate a mobile terminal, these techniques require known network references such as base station locations and measurement calibration values. The locations of base stations in a wireless network are usually known to a certain extent, e.g., within an error of a hundred meters. However, such a level of accuracy would produce significant errors when used in location determination of a mobile terminal. Thus, the accurate location of the reference point needs to be determined and verified for reliable location determination purposes.
Radio Frequency (RF) characteristics of transmitters and receivers also vary over time due to environmental changes. This introduces systematic biases and errors into radio measurements. These biases/errors also need to be removed from the radio measurements for reliable location determination purposes.
Typically, the network references need to be determined and characterized prior to location determination of the mobile terminal. To fix reference point locations, test engineers are sent to the field to conduct surveys by using other independent location techniques such as Global Positioning System (GPS). To compensate for time-varying biases/errors in radio measurements, test engineers also perform a repeat calibration procedure to determine these calibration values and in turn, subtract their effects from subsequent position calculations. In the description of this invention, “system biases” and “calibration values” for a base station are interchangeable terms. Field surveys and repeat calibrations significantly increase engineering complexity and operational costs, especially for large-scale wireless networks.
For scenarios in which a mobile terminal is capable of performing radio measurements, the key information on the network references, including base station locations and measurement calibration values, may be unavailable or inaccurate. This greatly diminishes the ability to determine the position of the mobile terminal. Therefore, there is a need for a system and related method that remove the constraints of known network references for mobile location determination.